An ad-hoc network has been put into practical use as one form of a network that includes a plurality of nodes. In the ad-hoc network, autonomous route selections are made at each node. That is, each node device (or communication device) in the ad-hoc network is provided with a function operated as a router or a switch. Each node device can recognize a neighboring network configuration by transmitting and receiving, for example, a message to and from its adjacent node device. Accordingly, adopting an ad-hoc scheme (in particular, a wireless ad-hoc scheme) allows a desired network to be configured by simply arranging node devices in an environment in which a network needs to be configured without providing a network management system that manages the entire network. Moreover, in the ad-hoc network, a node is readily added or deleted so that a network configuration can be readily changed.
In the meantime, in general, a network preferably has a bypass route (or a redundant route or a substitute route) so that communication can be continued even when a fault occurs. In particular, in wireless networks, a link may be temporarily disconnected depending on a radio wave environment, so it is important to confirm the presence/absence of a bypass route in advance.
As an example, in a network illustrated in FIG. 1, to transmit data from nodes A-E to a node GW, the data needs to be transmitted via a node X. That is, there is no bypass route between the node GW and the nodes A-E. A node such as the node X through which transmitted data needs to pass before reaching a particular destination may hereinafter be referred to as a “bottleneck node”.
In the network configuration illustrated in FIG. 1, when the node device X fails, the node devices A-E cannot transmit data to the node GW. In addition, when a link between the nodes X and Y is disconnected, the node devices A-E are also incapable of transmitting data to the node GW. That is, the node devices A-E have a risk of being isolated from the node GW. Accordingly, an operator who manages or administers the network needs to find a bottleneck node so as to properly provide a bypass route.
However, adding a relay node to form a bypass route increases the cost of the network. Thus, the operator needs to carefully add a relay node. Accordingly, a method is desired for precisely finding a bottleneck node.
In the ad-hoc network, however, it is difficult to correctly recognize communication routes within the entire network. Accordingly, in the ad-hoc network, it is not easy to confirm whether or not there is a bypass route for each communication route.
Providing a server computer that manages a network allows routing information of all nodes to be collected to analyze a network topology. However, in a network with many nodes, it takes a long time to collect routing information. In addition, in a wireless network, the state of links between nodes is unstable. As a result, when it takes a long time to collect routing information, a topology obtained by the server computer (i.e., a topology at the time of completion of the collecting of routing information) may not be identical with an actual topology.
As described above, in the prior art, it is difficult to precisely find a bottleneck node in a wireless ad-hoc network.
As a related art, a wireless communication device is proposed that forms an autonomous distributed wireless network by intermittently transmitting and receiving a specified communication management signal. The wireless communication device includes: a reception unit for receiving the communication management signal; an evaluation unit for evaluating a communication state of the wireless communication device in the wireless network based on a history of receiving the communication management signal by the reception unit, and a notification unit for providing a notification corresponding to an evaluation result of the communication state by the evaluation unit (e.g., Japanese Laid-open Patent Publication No. 2009-147646).
As another related art, a network control device is proposed that includes bottleneck estimation means for estimating as a bottleneck candidate a relay device with a transmission error rate of a transmission data link that is greater than a transmission error rate of a reception data link from among a plurality of relay devices in an ad hock network (e.g., International Publication Pamphlet No. WO2009/028185 (Japan Patent No. 4294723)).